PB1284 - α-Actin-1 deficiency influences platelet function and thrombus formation through a mitochondria-related mechanism

Background: α-Actinin-1 is an actin-binding protein expressed in nonmuscle cells, but mutations in this protein may cause congenital macrothrombocytopenia. Actin polymerization contributes to multiple distinct processes in mitochondrial biology, including mitochondrial damage, motility and fission.

Aims: To explore the mitochondria-related mechanism involved in the dysregulation of platelet functions and thrombosis caused by α-actinin-1 deficiency.

Methods: Using platelet-specific α-actinin-1 knockout (PF4-Actn1-/-) mice and control (Actn1f/f) mice, the platelet number, mean platelet volume and platelet function were determined, and thrombosis was induced both in vitro and in vivo. Mitochondrial morphology was observed by transmission electron microscopy, and mitochondrial functions were evaluated through flow cytometry and a Seahorse Extracellular Flux Analyzer in both a genetically modified murine model and 293T cells.

Results: We demonstrated that PF4-Actn1-/- mice exhibited reduced platelet counts, abnormal giant platelets and decreased platelet function. Furthermore, microfluidic assays revealed decreased thrombus formation in immobilized collagen matrixes at different wall shear rates (500 S-1 or 1500 S-1) in PF4-Actn1-/- mice. The occlusion time of the PF4-Actn1-/- mice decreased, as determined by FeCl3-induced carotid artery thrombosis assays. Laser injury-induced thrombosis in the cremasteric arterioles appeared to be suppressed in PF4-Actn1-/- mice. A greater survival rate was observed in PF4-Actn1-/- mice injected via the tail vein with collagen and epinephrine. In addition, the mitochondrial cristae of PF4-Actn1-/- mice underwent morphological changes. α-Actinin-1 deficiency impaired mitochondrial calcium mobilization, mitochondrial ROS production and the mitochondrial membrane potential, which led to energetic deficits and oxidative stress. Mitochondrial ATP production rates and the functions of the electron transport chain, as measured by a Seahorse Analyzer, were decreased due to α-actinin-1 deficiency.

Conclusion(s): Our findings showed that α-actinin-1 deficiency contributed to the inhibition of platelet function and thrombus formation through influencing mitochondrial bioenergetics.